1. Field of the Invention
This invention relates generally to optical communications, and more particularly to all-optical switching of fiber networks.
2. Description of the Related Art
A critical technology in enhancing speed and bandwidth in communication systems is All-Optical switching, a primary goal of the telecommunication industry. Optical cross-connects are the enabling devices for the planned all-optical communication networks. They connect high-capacity fiber optic communication links coming into a particular hub with any of hundreds of outgoing channels. In doing so they solve two major problems. First, they provide controlled connections among numerous intermediate links to create a continuous optical pathway between endpoints anywhere in the network, optimizing the stream of data and reducing the cost of service. Secondly, they protect the network in the event of catastrophic failure of an intermediate link by instantaneously re-routing a circuit. An all-optical network will be easier to manage and more reliable while reducing the cost of bandwidth.
There are several types of All-Optical switches known in the art. The classification of optical switches is presented in FIG. 1. Among them there are switches based on light birefringence phenomenon, switches utilizing light polarization in liquid crystals, switches utilizing bubbles in capillaries, electromechanical switches, and mirror-based switches.
Many 1xc3x97N switch architectures are based on a combination of two-state gates in a tree like structures. For N input channels N similar structures are required. It is clear that Nxc3x97N switch requires N2 gates. Moreover, in such a switch each of N output channels requires additional couplers and therefore increases both cost and optical losses in this switch architecture.
The operation of birefringent switches, typically based on lithium niobate or titanium niobate crystals, is polarization sensitive, and thus these switches require polarization-preserving optical fibers, and also require careful input/output waveguide mode matching in the optical system. Lithium niobate based switches have relatively large insertion loss and provide only a moderate degree of channel isolation. Besides, such switches require complicated fabricating processes. Examples of such switches can be found in the U.S. Pat. Nos. 4,976,505 and 5,946,116.
Liquid Crystal Optical Switches offer relatively high on/off ratios and relatively low optical insertion losses. But they require polarized light. Additionally, liquid crystal switches have certain environmental limitations including limited operating temperature range and environmental degradation. It is generally agreed upon that the technology lends itself only for small-size switching arrays. Examples of such switches can be found in publication Bawa et al., xe2x80x9cMiniaturized total-reflection ferroelectric liquid-crystal electro-optic switch,xe2x80x9d Appl. Phys. Lett., vol. 57, No. 15, pp. 1479-1481, Oct. 8, 1990 and in the U.S. Pat. No. 5,132,822.
Another architecture, based on waveguides and gas bubbles in fluid media, is described in the U.S. Pat. No. 6,055,344. At each switching point an input waveguide intersects an output waveguide at a fluid-filled trench. If the intersection is filled by liquid then the light passes straight through the intersection. When a gas bubble is placed in the intersection then light reflects to the output waveguide. It is obvious that an Nxc3x97N channel switch also requires N2 gates. Gas bubble based switches have certain environmental limitations including operating temperature range and environmental degradation. Insertion loss for such switches greatly depends on optical path and can vary many times within one switch. A similar architecture, based on waveguides and mirrors, is described in the U.S. Pat. No. 5,960,132.
Optical switch utilizing thermo-optical attenuators as the gates is described in xe2x80x9cSilica-based optical-matrix switch with intersecting Mach-Zehnder waveguides for larger fabrication tolerancesxe2x80x9d by M. Kawachi et al, Conference OFC/IOOC ""93, Feb. 21-26, 1993, San Jose, Calif. (U.S.A.), paper TuH4. Each input guide splits on two guides. After splitting each guide will have a gate, which can either open or close the guide. It can be shown that the total number of required gates for an Nxc3x97N switch is 2 N2.
Another technology is based on a sliding mirror between two or three fibers, which can potentially be used as a variable optical attenuator or as an optical switch in small-size switching arrays. See U.S. Pat. No. 6,031,946.
Another group of optical switches utilizes multi-state switching elements. One of the great advantages of open space architecture is that the light beams can physically cross each other without interference of the signals transmitted by both beams. The light beams carrying information are transparent to each other. This is a unique property of light, which allows building switches with absolutely different architecture not possible in the electrical wire world.
The majority of current open space optical switching technologies are based on MEMS micro-mirrors. Schematically this principle is shown in FIG. 2 The light beams 10 from the input fibers 12 are focused with collimators 14 on the first set of mirrors 16, where they are redirected, as shown in 18, onto a second set of mirrors 20, which in their turn are redirecting the beams 22 into required output collimators 24 and then to the fibers 26. Nxc3x97N optical switch based on this architecture requires 2N mirrors. Optical attenuation is in the range of 5 to 10 dB and they require at least two major optical alignments: between the transmitting array and the first mirror array and between the second mirror array and the receiving array. This architecture is complicated mechanically, optically and electronically.
Some of these MEMS micro-mirror arrays are based on surface micromachining technology. These devices have few disadvantages. The reported switching time is relatively slow. The optical losses are high. A large portion of these losses is inherent to this technology. For example, a non-flatness of the mirror is one of the sources of optical losses.
Other technologies use micro-mirrors based on bulk silicon micromachining. Bulk micro-machined mirrors with Gimbals suspension are inherently extremely fragile due to the relatively large mass of the mirrors, which are suspended by very thin beams. This results in low yield, high cost, and low reliability. See U.S. Pat. No. 5,629,790 incorporated fully herein by reference.
In another approach the switching or channel selection is achieved by means of a prism. Optical losses are moderate but the architecture and structure of the switch is complicated. See U.S. Pat. Nos. 5,999,669 and 6,005,993.
Another approach of redirecting the light beams between the transmitting and receiving arrays is based on lateral movement of the micro-lenses in front of collimators. However, it requires large space around the lens and the efficiency of the real estate utilization in the array is very low. See, for example: H. Toshiyoshi, Guo-Dung J. Su, J. LaCosse, M. C. Wu, xe2x80x9cMicrolens 2D Scanners for Fiber Optic Switchesxe2x80x9d, Proc. 3rd Int""l Conf. On Micro Opto Electro Mechanical Systems (MOEMS99), Aug. 30-Sep. 1, 1999, Mainz, Germany, pp. 165-167.
In electromechanical optical switches the input optical fibers are moving relative to the output optical fibers. Electromechanical switches don""t require mirrors and therefore, don""t require corresponding optical alignments and have smaller optical losses. However, macro actuators, for example step motors, are usually used in electromechanical switches as actuators. As an alignment of the fibers is critical in such systems, providing this precise and reproducible alignment with the motors is a big challenge. Another limitation of the electromechanical switches is that it is difficult to move simultaneously and independently more than one input fiber with respect to N output fibers. Besides, actuators used in these optical switches typically have only one degree of freedom, i.e. they allow circular motion of the fiber. Although these switches historically appeared first, they are usually 1xc3x97N switches, mechanically complicated, unreliable and slow. Examples of electromechanical optical switches are described in U.S. Pat. Nos. 4,378,144, 5,920,665.
Another optical switch is described in U.S. Pat. No. 4,512,036. In this switch, the end of the fiber is bent in two dimensions relative to a lens, which focuses the beam to a receiving lens. Piezoelectric actuators perform the bending of the fiber. Besides being costly, the dimensions of these beam steering units affect the overall size of the optical switch. As piezoelectric actuators have certain limitations in the displacement, this type of switch can be used only for relatively low port-count. The main disadvantage of this switch is that it is trying to combine different incompatible technologies in one device. They can not be integrated in one batch fabricating process. As a result, the technology of assembling is very complex, performance and reliability are low and expected cost is large.
An enabling development for all-optical systems is the concept of Optical MEMS. An acronym for Micro-Electro-Mechanical Systems, MEMS is a term used to describe a conceptxe2x80x94Microsystems that monolithically integrate microstructures, sensors, actuators or optical components, like mirrors, lenses, couplers, etc., with associated mechanical, optical and electronic functions. MEMS are now used throughout the world in an ever-expanding range of applications in automotive, industrial and consumer products. Communication technology and specifically optical communication will be revolutionized with Optical MEMS. One of Optical MEMS switches is disclosed in this patent application.
There is a need for an optical switch with a larger number of switching channels that have the same optical loss. There is a further need for an optical switch with smaller optical loss in each switching channel.
Accordingly, an object of the present invention is to provide an optical switch with a larger number of switching channels with the same optical loss.
Another object of the present invention is to provide an optical switch with smaller optical loss in each switching channel.
Yet another object of the present invention is to provide an optical switch with faster switching.
Still another object of the present invention is to provide an optical switch with lower cost of switching per channel.
Yet another object of the present invention is to provide an optical switch that has higher reliability.
A further object of the present invention is to provide an optical switch with lower sensitivity to vibrations.
Another object of the present invention is to provide an optical switch with lower temperature sensitivity of optical switching.
A further object of the present invention is to provide a smaller size optical switch.
Yet another object of the present invention is to provide an optical switch with a simpler architecture. Another object of the present invention is to provide an optical switch with an improved movable microstructure.
Yet a further object of the present invention is to provide an optical switch with a more effective actuator of movable microstructure.
Another object of the present invention is to provide an optical switch that has higher sensitivity sensors for a closed loop control system.
Yet another object of the present invention is to provide a multi-position open loop control system for an optical switch.
A further object of the present invention is to provide a higher level of integration of different components for an optical switch.
Still another object of the present invention is to provide a higher level of integration of different MEMS, electronic and micro-optical components of an optical switch.
Yet another object of the present invention is to provide optical switch with fewer components.
Another object of the present invention is to provide an optical switch that has less optical alignments of components.
These and other objects of the present invention are achieved in an optical switch that includes a plurality of transmitting devices with a plurality of optical fibers that each have a distal end. A plurality of focusing devices are included. Each distal end of a fiber is coupled to at least one focusing device. A plurality of receiving devices are provided. At least a portion of the distal ends of the optical fibers move in three orthogonal and at least two angular dimensions to direct output beams from the plurality of transmitting devices to the plurality of receiving devices.
In another embodiment of the present invention, a method for optical switching between input fiber channels output fiber channels provides a plurality of transmitting devices including a plurality of optical fibers and a plurality of receiving devices including a plurality of optical fibers. Moving at least a portion of the distal ends of the optical fibers in three orthogonal and at least two angular dimensions to direct output beams from the plurality of transmitting devices to the plurality of receiving devices.